This invention relates to a method of manufacturing a rotor assembly of a dynamoelectric machine, and more particularly relates to an improved method of treating a squirrel cage rotor assembly for resisting corrosion on the exposed surfaces of the rotor assembly.
Conventionally, rotor assemblies of dynamoelectric machines (and in particular fractional horsepower motors) are treated so as to protect their exposed surfaces (i.e., those surfaces liable to corrode or rust) from rust or other corrosion which tends to form thereon. It has been found that a sufficient quantity of corrosion or rust on the outer surfaces of a rotor body will bridge the air gap between the rotor and the adjacent teeth of the stator core resulting in arcing between the stator and the rotor and thus preventing the motor from starting. Conventionally, prior art rotors had a zinc chromate solution applied to their outside surfaces so as to inhibit the formation of rust or corrosion. Also, several prior art rotor treatment processes required several intermediate process steps which, of course, were time consuming and costly in the manufacture of rotor assemblies.
More specifically, the method of this invention is an improvement of the method disclosed in my prior U.S. Pat. No. 4,113,518 issued Sept. 12, 1978 and assigned the the assignee of the present invention. In my prior patent, a method of treating a rotor assembly is described in which the rotor assembly is heated to a temperature (e.g., about 900.degree. F. or 482.degree. C.) sufficient to permit shrink fitting of the rotor core on the rotor shaft. The rotor assembly is then cooled in a water quench bath. The rotor assembly is then cleaned, rinsed, pickled, and treated with a surface oil retention solution (e.g., a water solution of zinc phosphate). Then, the rotor assembly is rinsed, dried, and finally dipped in a solvent based, water displacing oil which is preferably maintained at an elevated temperature (e.g., about 180.degree. F. or 84.degree. C.).
Among the several objects and features of this invention may be noted the provision of an improved method or process of manufacturing a rotor assembly which is faster, which involves fewer manufacturing steps, and which results in a corrosion resistant treatment for the rotor assembly better than prior rotor corrosion treatment methods;
The provision of such a method which requires appreciably less capital investment than other comparable rotor treatment process to incorporate in a manufacturing assembly line;
The provision of such a rotor treatment process which consumes less energy than prior rotor treatment processes;
The provision of such a method in which surfaces between the rotor laminations as well as the visible surfaces of the rotor assembly are treated against corrosion;
The provision of such a method which eliminates the necessity of having to treat the exposed surfaces of the rotor assembly with another corrosion resistant coating material, such as an epoxy coating or the like;
The provision of such a method in which one heating step of the rotor assembly may be utilized for both shrink fitting of the rotor core on the rotor shaft and for the corrosion treatment of the core; and
The provision of such a method which effectively prevents or inhibits the formation of corrosion for extended periods of time in high moisture environments.
Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.